1. Field of the Invention
The present invention relates to a hard disk drive adopting Partial Response signalling & Maximum Likelihood (PRML) detection, and more particularly to a method for laying out an adaptive zone by utilizing the pulse width of a signal read by a head.
2. Description of the Related Art
The mechanism of a hard disk drive widely used as an auxiliary memory device consists of a magnetic head to read or write data from or on a magnetic disk, a microprocessor, and a read/write channel circuit connected to the microprocessor.
In the read/write channel circuit of the hard disk drive, a peak detection method is adopted as a data pulse detection method due to the feature of magnetization inversion. Recently the method of partial response signaling & maximum likelihood detection (hereinafter referred to as `PRML`) originated from digital communication is applied to a hard disk drive due to demand for a hard disk drive of high speed and capacity, and accordingly the related technology has been researched actively. U.S. Pat. Nos. 5,585,975 and 5,563,746, both to Willaim G. Bliss, are examples of a read/write circuit using a PRML method and also teach the use of PR4, EPR4 and EEPR4 in a PRML method.
For making the most use of an advantage of the PRML, a read signal from disk should be passed through a specially designed equalization filter. The function of the equalization filter is to shape a wave utilized easily by a maximum likelihood sequence estimation detector (hereinafter referred to as `MLSE`). The equalization filter is achieved by combining an analog filter and a digital filter, wherein the digital filter is adopted essentially and the quantity of tap of the filter is large enough for shaping a more correct wave.
I have determined that it is necessary to adjust the pulse width of a read signal for obtaining wanted sampling values at given sampling times. For this purpose, an equalizer is used in a hard disk drive adopting the PRML method. However the pulse width of a read signal is varied due to different features of each head when multiple platters are adopted as a way of increasing data capacity in a conventional hard disk drive and accordingly multiple heads are installed above the platters. The pulse width of the read signal from the head is varied according to the flying height of the head and the position of a track arrayed in concentric circles on a disk platter. And an error occurs by misequalization phenomenon when the pulse width of a signal read from the head is not adjusted. Hence, a number of data errors are caused in reading data in a hard disk drive adopting the conventional PRML method.